1. Field of the Invention
The present invention relates to a line interface for connecting a communication line with a communication terminal.
2. Related Background Art
A method for connecting a communication terminal to an ISDN (integrated services digital network) has been known as a method for connecting the communication terminal to the communication line. The connection method is recommended by the CCITT as I.460 Series Recommendation. The connecting configuration is shown in FIG. 5.
It comprises a network terminator NT which terminates a subscriber line and a private bus, a terminal adaptor 1 for converting an existing interface to an ISDN user network interface, and a terminal equipment TE2 having an interface of an existing V series or X series. A connecting point of the terminal equipment TE2 and the terminal adaptor 1 is called an R reference point, and a connecting point of the terminal adaptor 1 and the network terminator NT is called a T reference point.
The terminal adaptor 1 has a function to convert a protocol for the terminal equipment TE2 to a protocol for the network terminator NT, a function to convert the protocol for the network terminator NT to the protocol for the terminal equipment TE2, and a function of rate adaption at the points R and T.
In the prior art system, a conventional G3 facsimile machine has an interface to connect to the PSTN (public telephone network) and it is not a subject of the I.460 Series Recommendation. Accordingly, it cannot be connected to the ISDN as it is.
U.S. patent application Ser. No. 151,309 filed on Feb. 1, 1988 relates to an ISDN communication terminal.